The present invention relates to a method and an apparatus for supporting a sheet of glass and, more particularly, to such a method and apparatus in which a sheet of glass may be supported during heating and cooling operations without significantly affecting the surface of the glass sheet, and without providing undue thermal insulation over the surface of the glass sheet.
In various glass forming and treatment operations, such as those for forming and tempering sheets of glass for use in automobiles, it is necessary that the sheets of glass be supported and transported to a succession of stations. At some stations, the glass sheets may be heated and then formed. At other stations, the glass sheets may be heated and then quickly chilled to temper the glass. In tempering sheets or panels of glass, it has been common in the past to support glass sheets near their upper edges by tongs which are suspended from a carrier. The carrier transports the glass sheets into and out of a heat treating furnace. U.S. Pat. No. 2,710,493, issued June 14, 1955, to Glynn, discloses such a glass carrier arrangement. In the Glynn tong arrangement, a metal rod is inserted between the arms of the tongs, prior to conveying the tongs, and a glass sheet carried by the tongs, into a heat treatment oven. This rod avoids the problem of the tongs biting too deeply into the glass after the glass is softened by the heat treatment process. The rod blocks the arms from moving too close together, thereby preventing the jaws of the tongs from imbedding themselves further into the glass when it becomes softened in the furnace.
Several difficulties are encountered with a tong support arrangement such as disclosed in the Glynn patent. Since the jaws of the tongs include round pointed screws which contact the glass sheet, unsightly indentations are made on both sides of the glass sheet as it is heated in the oven, the rod extending between the arms of the tongs not withstanding. Further, in view of the rather substantial surface area of the tongs in contact with the glass surface during heating and chilling operations, the tongs tend to thermally insulate the sheet of glass in the area of contact from the heating and cooling cycles, thus preventing the glass from being tempered in this region.
It is seen, therefore, that there is a need for a method and apparatus for supporting a sheet of glass in which marring of the surface of the sheet is minimized. Further, there is a need for a method and apparatus for supporting a sheet of glass in which the glass is not significantly thermally insulated, thereby facilitating heating and cooling of the glass sheet.